Sympathoadrenal and Metabolic Responses to Graded Exercise in Rats

Abstract

We have recently developed a tiny metabolism chamber, including a treadmill, for steady-state investigations in exercising rats. In the present study, we evaluated the sympathoadrenal and metabolic responses to graded exercise in seven rats with chronically implanted arterial catheters. A procedure that minimizes the effect of excitement reactions was used. The concentrations of adrenaline and noradrenaline in plasma and those of glucose and lactate in blood increased with increasing running speed, whereas PaCO2 decreased. PaO2, PH, and hematocrit remained unchanged throughout the experiment. In the first 3 min after exercise, blood glucose increased further, whereas the concentrations of adrenaline and noradrenaline decreased considerably. Three rats running at hypoxia (PaO2 = 61 mmHg) as well as at normoxia had higher noradrenaline, glucose, and lactate concentrations at hypoxia. In three other rats running at hyperoxia (PaO2 = 445 mmHg) as well as at normoxia, the only uniform difference was lower heart rates at hyperoxia. In conclusion, sympathoadrenal activity increases with increasing work intensity in rats. The marked changes in blood glucose concentration indicate that this parameter is not accurately regulated during short-term exercise. Finally, the rapid post-exercise changes demonstrate that evaluation of exercise responses has to be based on determinations made during exercise.